Through 575 games of Rondo's career, he never made more than two 3PT FGs - Game 576: 3, Game 577: 4.

Over 7 seasons he attempted 5 threes in a game just once, this year he's done it 3 times in 10 games.

3PT field goal attempts per game: Career 0.76, this season 2.9.

3PT field goal percentage: Career 25%, this season 38%.

And here's my analysis from two days ago (although reason #1 now appears less likely after what we just saw in Rondo's 10th game back):

Off the top of my head I see three possibly explanations for this:
1. It's a coincidence. Nine games is a tiny sample size... Maybe this is just a weird anomaly.
2. He spent the past year of his rehab working on shooting from beyond the arc, and now he's trying to show that off.
3. Rondo is the Captain, and this is his team now. He's the go to guy, and doesn't have any other veterans to differ to. Nobody else is going to demand the ball from him when it's time to shoot.

My guess is the answer is a combination of all three. Regardless, this is something to keep an eye on going forward.

Also, like we've seen with Jared Sullinger, Brad Stevens definitely encourages three-point shooting. From Scott Souza of the Metro West Daily News: